(Invited) Self-Terminated Electrodeposition Reactions

In a recent publication Pt deposition at negative potentials revealed an unanticipated self-terminating characteristic that enables controlled deposition of Pt monolayer films from a K₂PtCl₄-NaCl electrolyte. In the case of Pt, the deposition reaction is quenched at potentials just negative of proton reduction by alteration of the double layer structure and adsorption properties induced by a saturated surface coverage of underpotential deposited hydrogen, (H_upd). The surface may be reactivated for Pt deposition by stepping the potential to more positive values where H_upd is oxidized and fresh sites for adsorption of PtCl₄^2- become available. Periodic pulsing of the potential enables sequential deposition of additional Pt layers to fabricate films of desired thickness relevant to a range of advanced technologies in manner that is tantamount to wet atomic layer deposition (ALD).  In the presence of iron group metal the H_upd induced suppression is lifted by underpotential deposition of the iron group metal as revealed in voltammetric studies of singular surfaces and thin film deposition studies of the binary Pt_100-xNi_x and Pt_100-xCo_x alloy. Bulk alloy formation is facilitated by ongoing Pt deposition that incorporates the iron group metals in accord with the excess enthalpy of alloy formation. This talk will present an update on the exploration of the generality of self-terminating deposition reaction to other chemical system such as Ir and other transition metals.